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The Palisades Creek branch of the East Kaibab monocline in Grand Canyon National Park, Arizona, can be divided into three structural levels with contrasting styles of deformation: a lower level composed of a vertical fault, the Palisades fault, and a sharp synclinal bend; an intermediate level characterized by a tight, steep monoclinal flexure; and an upper level dominated by an open monoclinal flexure. The three styles of deformation apparently were controlled by a combination of position relative to the fault and of structural behavior of various rock units. The profile of the monocline at depth might have been estimated by study of the profile of the monocline at the surface, but only if data concerning structural units were available.

Study of the internal strain and accurate mapping of the gross structure provide fundamental data for a theoretical model. Analysis of small-scale structures, including faults and folds as well as calcite twinning and thicknesses of rock units, indicates the internal strain of the rocks during monoclinal flexuring. Most strain indicators are consistent and imply shortening subparallel to layering at all levels within the monocline. An accurate cross section and local measurements of thicknesses of units indicate that layers in the monocline have changed thickness appreciably.

A general model of monocline formation must incorporate effects of layer-parallel shortening as well as differential vertical displacement along the underlying fault. Such a model is presented in Part II (this volume).

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